Spasticity is a disorder in which certain muscles are continuously contracted. Symptoms include exaggerated reflexes (hyper-reflexia), muscle spasms and fixed joints. Spasticity is difficult to quantify because of its various components, however, most researchers quantify its major component, hyper-reflexia. Spasticity may be as mild as a feeling of tight muscles, or may so severe as to produce uncontrollable, painful spasms of the legs or other extremities. Spasticity can interfere with movement and speech. Untreated spasticity can lead to frozen or immobilized joints and pressure sores. It prevents recovery of proper motor behavior after injury or disease.
Spasticity can arise as a consequence of several conditions including spinal cord injury (SCI), stroke, cerebral palsy, brain injury and multiple sclerosis. Spasticity in patients with SCI is particularly difficult to manage. Exercise and stretching are advocated as management tools, but these activities are difficult to perform for most patients. The patients often do not appreciate the long-term benefits from stretching and exercise, an effective stretching or exercise program takes time to perform, and individuals with paraplegia or tetraplegia often need assistance to perform such a program. These same barriers also often exist for other patients with spasticity, including stroke victims, brain injury victims, cerebral palsy patients and multiple sclerosis patients.
Drugs available for the management of spasticity include baclofen. Baclofen is a GABAb receptor agonist. Baclofen basically acts to potentiate inhibition mediated by presynaptic GABAb receptors. The rationale for the use of baclofen for the treatment of spasticity was due to the assumption that excessive reflexes were induced in SCI by the elimination of presynaptic inhibition from nerve fibers descending from the brain. SCI has been thought to lesion these descending fibers, rendering the spinal cord hyper-reactive. Baclofen is thought to restore some of that inhibition. However, baclofen taken orally unfortunately increases inhibition throughout the brain, leading to sleepiness and weakness. In order to avoid such side effects (which reduce the ability of patients to concentrate), baclofen pumps were designed to inject the drug directly into the spinal fluid, usually in SCI victims and cerebral palsy patients. These pumps avoid the soporific effects of oral administration but are dangerous, have a limited lifetime (requiring repeated surgical implants) and are very expensive.
New treatments for spasticity are needed.